Field of the Invention
Embodiments of the present invention relate to a display device, and a printed circuit board for supplying a driving voltage and a base voltage to the display device.
Description of the Related Art
An organic light emitting display device, which has recently attracted attention, uses a self-emitting organic light emitting diode (OLED). Such an organic light emitting display device therefore has advantages including a high response speed and increased contrast ratio, light emitting efficiency, brightness, and viewing angle, as compared to other display device technologies.
Each sub-pixel disposed in the organic light emitting display device typically includes a driving transistor configured to drive an OLED, a switching transistor configured to transfer a data voltage to a gate node of the driving transistor, and a capacitor configured to maintain a certain voltage for one frame time.
The driving transistor within each sub-pixel typically has characteristics such as a threshold voltage, mobility, etc. Such characteristics may vary by sub-pixel.
Further, as a driving time is increased, the driving transistor may degrade and its characteristics may change. A difference in degradation between sub-pixels may therefore cause variations in characteristics between sub-pixels.
The variations in characteristics between sub-pixels may cause a brightness variation and thus brightness unevenness of the organic light emitting display device. Accordingly, a technology for measuring characteristics of each sub-pixel and compensating therefor has been developed.
Meanwhile, the measurement or compensation for characteristics of a sub-pixel should be performed without being recognized by a user. For example, if the OLED emits a light in response to a voltage supplied to the driving transistor for measuring the characteristics, an image irrelevant to image data may be displayed on a pixel, and the pixel may be recognized as an error by the user.
In order for the OLED not to emit a light during the measurement of characteristics, the display device may supply a higher voltage as a base voltage than the voltage supplied when the OLED is driven. For example, typically, when the OLED is driven, the display device may supply a ground voltage as a base voltage. However, during the measurement of characteristics, the display device may supply a higher voltage as a base voltage. Thus, it is possible to suppress light emission of the OLED during the measurement of characteristics.
However, when a voltage different from the ground voltage is supplied as a base voltage, switching noise from the power supply may influence measurement of the characteristics.
Generally, a switched mode power supplier (SMPS) is used to generate direct-current (DC) power. A DC voltage generated in the SMPS may undesirably include a switching noise, which is also referred to as a ripple noise. The switching noise may be inevitably generated according to a driving method of the SMPS.
This switching noise can influence the measurement of characteristics of the display device. For example, there may be a parasitic capacitance between a line for supplying a base voltage to the OLED and a line for measuring characteristics. The above-described switching noise may be propagated from the line for supplying the base voltage to the line for measuring characteristics through this parasitic capacitance, and thus influence measurement of the characteristics.